Process fob washing glass articles



' Patented July 4, 1950 PROCESS FOR WASHING GLASS ARTICLES IN ALKALINE SOLUTIONS Leslie R. Bacon and Walter F.

Wegst, Wyandotte,

Mich., assignors to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan No Drawing. Application January 30, 1948, Serial No. 5,496

4 Claims.

The present application is an improvement in the process disclosed in U. S. patent application Serial No. 425,804 filed January 6, 1942; (now U. S. Patent No. 2,447,297) in which we are coapplicants with Thomas H. Vaughn. The aforesaid patent application discloses a process for cleaning glass articles such as beverage bottles, by washing them in a zincated alkali solution, 1. e. one comprising free or uncombined caustic soda and a small proportion of a substantially caustic soda-soluble zinc compound. The zinc compound, which-preferably is zinc oxide or zinc sulfate, acts as an inhibitor in preventing the solubilizing or scuffing action of the caustic soda on the glass.

It has been stated in the aforesaid patent application that the protective action imparted by treatment with zincated alkalies against the solution of the glass substance continues its restraining action when bottles are subsequently exposed to the solubilizing action of non-zincated alkalies although the effectiveness of this protective action diminishes with increasing exposure." We have now discovered, that although the presence of a glass attack-inhibiting agent (such as the caustic soda-soluble zinc compounds of the aforesaid application Serial No. 425,804 or the caustic soda-soluble beryllium compound of U. 8. Patent No. 2,419,805 issued April 29, 1947) acts to retard the glass solubilizing action of the caustic soda solution, a certain percentage of the bottles so washed have been found to show a misty or cloudy appearance which renders them subject to rejection by the bottle washing machine inspector. V

Pursuant to the above quoted statement from patent application Serial No. 425,804, we have now discovered that a two-stage washing treatment of the bottles overcomes this 1ast stated difficulty. In the first stage wherein most of the soil is to be removed, the bottles are washed in an alkaline caustic soda solution containing the glass attack-inhibiting agent. In the second stage, the bottles are washed in a relatively weaker caustic Soda solution containing no inhibiting agent. Although we do not wish to limit ourselves to any scientific principle or theory for our invention, it is believed that the first stage washing of the bottles in the caustic soda-inhibiting agent solution results in the formation of a minute. hydrophobic protective film on the glass surface, and the second stage washing in the inhibitor-free caustic soda solution brings about just enough of a controlled solubilizing action and removal of this protective film as to leave a u hydrophilic, bright, glass surface. For brief and convenient reference, We have thus called our invention a controlled etching process.

The following description sets forth in detail the method exemplifying and illustrating the principle of our invention, whereby it may be readily understood and practiced by those skilled in the art.

When glass bottles or beverage containers are returned to the bottling plant for washing prior to re-filling, they are ordinarily passed through either soaker type or hydraulic type washing machines. In a large machine of the soaker type a typical cycle of operations would consist in the following:

Prerinse with warm water Soak at 140 F. in alkaline solution of 3.0-3.5%

caustic soda content Soak at 155 F. in alkaline solution of 2.5-3.0%

caustic soda content Water rinse at lower temperature, as 125 F Water rinse at lower temperatures, as F Internal and external brushing One or more internal and external cool water rinses Internal chlorination rinse In-practice the number and sequence of cleansing steps is subject to considerable variation, however, and this is true also of temperatures and concentrations of solutions employed. The step .of chlorination is most commonly employed in the washing of dairy bottles.

The practicable ranges of temperature and concentration for the alkaline solutions are usually taken to be -165" F. and l-5% caustic,

as hereinafter defined. The efiects of soaking time, alkaline concentration and temperature are interrelated in the sense that increased temperatures and/or concentrations diminish the soaking period required to attaina given standard of cleansing and germicidal performance. It is known further that increases in temperature of the alkaline solutions are reflected in increased scufling action and it is generally true that within the practicable economic limits increased concentrations are reflected in increased corrosion of the glass substance and scufling action. The period of exposure of bottles to the detergent solutions will usually run upward of 5 minutes per cleansing operation using soaker type machines.

Hydraulic type machines operate on the principle of projecting streams of alkaline solution and rinse waters at high velocity upon the bottles. Due to the vigorous mechanical action the practicable concentrations of and exposures to strongly alkaline solutions may run somewhat lower than for soaker type machines.

In either type machine, the alkali content or the washing solutions is maintained by suitable additions (make-up) from time to time. Control in the field may be exercised through indicating meters or by simplified chemical test methods. One common basis for controlling alkali concentration is the determination of actual caustic soda content, the practicable ranges of which may be taken to be 1-5%, dependent on other conditions hereinbefore referred to.

Now, according to our invention, we incorporate a sufliciently effective amount of a glass attack inhibitor, such as a caustic alkali-soluble zinc, beryllium, or aluminum compound, in the caustic soda solution in the first soaking tank, or in the solution in the hydraulic type machine which is first applied to the bottles. The strength of the caustic soda solution in this first washing stage should be relatively strong, such as 3% or greater by weight of free, uncombined NaOH. The glass attack-inhibiting agent, or caustic soda-soluble metallic compound, is preferably present in an amount up to 20% by weight of the total caustic soda present (viz: up to 20% by weight sodium zincate, sodium berylliate, or sodium aluminate). As disclosed in the above mentioned patent application Serial No. 425,804

and Patent No. 2,419,805, the percentage range content of caustic soda soluble-zinc compound is from 1.5 to 7.6% by weight, in terms of ZnO equivalent content, of the caustic soda present; and the caustic soda soluble-beryllium compound percentage range is 0.05% to 11.4% by weight in terms of BeO equivalent content on the basis of NaOH present.

In the second washing stage, or in the soaker tank or tanks following the first alkaline washing stage, we place a relatively weaker caustic soda solution containing no glass attack-inhibiting agent. The NaOH content of the washing solution in the second stage operation should be in the amount of 0.3% to NaOH content. Additional amounts of water softening alkaline salt, such as: sodium carbonate, sodium silicate (i. e. one having a l/l to 2/1 NazO/siOz mol ratio), trisodium phosphate, sodium tetraphosphate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate, can be incorporated in the second stage washing solution and in an amount up to 40% by weight of the total NaOH-alkaline salt content.

By way of this specific example, we have found the following two-stage washing solutions, at the concentration and temperatures below stated, to give excellent results in commercial practice.

A four-tank, commercial, soaker-type bottle washing machine, operating on standard Coca- Cola bottles was employed. A caustic soda-zinc compound material was made up having the following composition:

Per cent by weight Caustic soda (anhydrous) 97.2- ZnO 2.8

The above composition was added to the first and second tanks of the bottle washing machine in amounts to give the following NaOH content determined by titration to phenolphthalein endpoint:

Per cent by weight NaOH Tank No. 1 3.6 Tank No. 2 4.0

The temperature oi tank No. 1 was maintained at approximately 137 F. and tank No. 2 at approximately 156" F.

, The following caustic soda inhibitor-free composition was then prepared:

Per cent by weight Caustic soda (anhydrous) Sodium tetraphosphate (anhydrous) 20 This latter composition was added to tank No. 3 and in amounts sufficient to give a caustic soda content of 0.34% by weight, as determined by phenolphthalein end-point. The temperature of the solution in the third tank was 132 F.

Tank No. 4 contained rinse water at 83 F.

A record as kept of approximately 735,000 bottles wash. a in this machine, respectively, by our above described controlled-etching" process, and by the process in which NaOH-ZnO composition alone was used. In the operation of our "controlled etching process, on inspection for mistiness or cloudy appearance, only 0.2 bottles per thousand were rejected. By way of comparison, and in the same washing machine in which an equivalently strong caustic sodazinc compound inhibitor solution alone was used in the washing operation, 1.1 bottles per thousand were rejected on inspection.

It will be thus seen that in actual, commercial operation, our invention produced over 5 times greater improvement, or reduction in the number of bottles rejected for cloudiness, mistiness and insuiiiciently bright appearance.

Equivalent modes of practicing our above described invention may be employed provided that they are within the scope of the appended claims.

We, therefore, particularly point out and distinctly claim as our invention:

1. The method of washing glass articles which comprises first washing in an aqueous solution containing 1-5% by weight of free uncombined caustic soda and up to 20%, on the NaOH content basis, of a glass attack inhibitor, and then washing in an inhibitor-free solution containing 0.3 to 1.5% caustic alkali.

2. The method of claim 1, wherein the glass attack inhibitor is selected from the group consisting of a caustic soda-soluble compound of zinc, beryllium and aluminum.

3. The method of claim 1, wherein the glass attack inhibitor is 1.5 to 7.6% in terms of ZnO equivalent, of sodium zincate, on the NaOH content basis.

4. The method of claim 1, wherein the glass attack inhibitor is 0.05 to 11.4% in terms of BeO equivalent, of a caustic soda-soluble beryllium compound, on the NaOH content basis.

LESLIE R. BACON. WALTER F. WEGST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD OF WASHING GLASS ARTICLES WHICH COMPRISES FIRST WASHING IN AN AQUEOUS SOLUTION CONTAINING 1-5% BY WEIGHT OF FREE UNCOMBINED CAUSTIC SODA AND UP TO 20%, ON THE NAOH CONTENT BASIS, OF A GLASS ATTACK INHIBITOR, AND THEN WASHING IN AN INHIBITOR-FREE SOLUTION CONTAINING 0.3 TO 1.5% CAUSTIC ALKALI. 